The present invention is concerned with the detection and determination of oxygen permeation into enclosed containers, particularly transparent containers constructed of polymeric material.
A good barrier to oxygen is critical to ensuring retention of quality in packaged foods and beverages. The permeation of oxygen into enclosed containers, such as polyethylene-terephalate (PET) bottles, having foodstuffs therein often causes spoilage of the foodstuff. It is common practice for the food industry to test for oxygen permeation into food packages to help determine product shelf-life. One common example is transparent bottles constructed of polymeric material and containing juice drinks. While the present invention is specifically described with respect to such containers, the invention is applicable to all forms of containers which are intended to house oxygen-sensitive products.
The conventional ASTM method (S1307-90) for measuring oxygen transmission rates utilizes a gas-flush system, such as the Mocon Ox-tran system. The Mocon Ox-tran 2/60 oxygen permeability testing instrument is a gas flushing system on which empty containers are mounted on the machine and flushed with nitrogen carrier gas. The oxygen passing into the container is carried to a coulometric detector, where the oxygen is quantified in units of cc packagexe2x88x921 dayxe2x88x921.
The present invention, in one aspect, provides a novel, non-invasive, quantitative method of determining the oxygen permeance into a sealed transparent container containing an aqueous solution. The present invention makes the determination in its intended state, namely as a container for a liquid system. In accordance with one aspect of the present invention, there is provided a non-invasive quantitative method of determining the oxygen permeance into a sealed container, which comprises providing a colorless aqueous solution of a reduced form of indigo-carmine dye in the sealed container, and determining the intensity of color development of the indigo-carmine dye over time as a measure of the oxygen permeation into the sealed container.
In another aspect, the present invention provides a novel, non-invasive, qualitative method of determining the location of oxygen permeation into a sealed container. In accordance with another aspect of the present invention, there is provided a non-invasive qualitative method of determining the location of oxygen permeation into a transparent sealed container, which comprises providing an immobilized aqueous solution of a reduced form of indigo-carmine dye in the sealed container, and observing the location of color development of the sealed container as a determination of the location of oxygen permeation into the container.
The present invention is based on in-situ development of color by oxidation of the reduced form of indigo-carmine dye in aqueous solution by oxygen permeation into the transparent container. As oxygen enters the packaging system, the reduced form of the indigo-carmine dye becomes oxidized, changing from colorless to blue and deepening with intensity with increased accumulation of oxygen ingress. The overall intensity of color development within the sealed container can be measured using a spectrophotometer and the sealed container. The degree of color development is used to determine the extent of the oxygen permeation into the container over time.
The indicator system may be immobilized in a gelled form, so that the color formation is localized to the areas of the bottle where there is oxygen permeation. The latter information is useful in the design of bottles or other containers to minimize such oxygen permeation and to locate failure points of the package.